Method and apparatus for stratospheric and space structures

ABSTRACT

The high-altitude balloon has a skin made of nearly evacuated electrostatically inflated cells which provide thermal insulation to minimize heat loss from the gas in the balloon, while transmitting heat from the sun to heat the gas. The lower surface of the balloon is reflective to microwave or laser beams. A stable array of the balloons is maintained at a high altitude and is used to facilitate communications in a world-wide communications system. Ascent of the balloon is well controlled and weight is minimized by starting with lighter-than-air gases in liquid form, releasing a lifting gas into the craft, and then using the empty containers to store the remaining gas when the balloon is aloft.

This invention relates to stratospheric and space structures and methodsand particularly to inflatable objects such as high-altitude balloonsand components thereof; electrostatically inflatable structures andmethods and communications systems and methods utilizing same.

Current global communications systems use land lines, radio towers, andsatellites for communications within populated areas and between remotelocations. Each one of these methods has drawbacks.

New land lines become extremely expensive to install in denselypopulated areas due to the high congestion and the high cost of“right-of-ways.” Land lines may not justify the investment in sparselypopulated remote locations where distances are greater and revenues areless.

The range of radio towers are fundamentally limited by the curvature ofthe Earth, natural terrain features, atmospheric conditions, andman-made structures. The high cost of tower construction may also beprohibitive in sparsely populated remote locations.

The launch cost for satellites is exceptionally high. Satellites provideline-of-sight coverage over wide areas, but also have fundamentaltechnical limitations. Geosynchronous satellites are very high above thesurface of the Earth (i.e., approximately 22,241 statute miles).Propagation delays are significant and high-gain antennas are requiredto obtain reasonable signal-to-noise ratios.

Low Earth Orbit (LEO) satellites circle much closer to the Earth'ssurface (200-500 statute miles). However, because their orbit is soclose to earth they must travel much faster relative to the Earth'ssurface to stay in orbit. Satellites in LEO speed along at approximately17,000 miles per hour and circle the Earth in about 90 minutes. A largenumber of LEO satellites are required to provide continuous coverageover a specific location on the surface.

It is believed that there are numerous projects currently under way byNASA and private industry to develop long-duration, high-altitudeballoons and aircraft for use in ground-to-ground communications orscientific missions. Many of these projects are based on designs thatare intended to carry heavy payloads to high altitudes.

These altitudes are well above the ceiling of commercial aircraftflight. The Lockheed SR-71 is believed to hold the high-altitude recordfor non-rocket, jet-powered aircraft, at 85,068 ft. It is believed thatNASA's solar powered Helios experimental aircraft reached an altitude of96,500 ft., in 2001, and that the TIGER balloon, for cosmic radiationresearch, reached an altitude of 133,000 ft., in 1997. NASA's Ultra LongDuration Balloon (ULDB) is intended to reach an altitude of 115,000 ft.and stay aloft for 100 days with a 3,500-lb. payload. So far, the ULDBis believed to have reached an altitude of 95,000 ft. The ULDB is verylarge and expensive. It has a height of 500 ft., 20 acres of compositeskin, and 20 miles of seams.

One of the most significant problems for high-altitude aircraft andballoons is maintaining altitude during night time. Helios uses solarcells to store energy during the daytime. Stored energy is used tosustain an array of propellers at night. It is understood that the ULDBmaintains its altitude at night by allowing the balloon to beover-pressured during the day. This approach requires a very strong andnon-elastic skin (i.e., the balloon has a constant volume).

A new balloon concept is needed that maximizes the altitude, maintainsthe balloon's altitude at night, stays aloft longer, and cost less tomake. A global communications system concept is needed that providescontinuous coverage over the entire planet with a reasonably affordablenumber of High-altitude reflectors. If this capability can be realizedon a global scale, then many people can have ready access tohigh-bandwidth communications. The effect on society would be profoundlypositive: benefiting the economies; protecting the environment; andimproving the human condition.

In accordance with the present invention, the foregoing objectives aresatisfied by the provision of a ultra-light, moderate cost, highaltitude balloon with a skin, preferably comprised of electrostaticallyinflated insulators which help govern and control the unwanted loss ofheat from the balloon interior, and a communication system and methodutilizing an array of such balloons as reflectors.

Also provided by the invention is a new building block for use instratospheric and space structures such as balloons and space vehicles,satellites, etc., and in other very low-pressure ambient conditions.This building block is a closed container with flexible walls withopposed conductive internal surfaces within which a positive or negativeelectric charge is established which causes the walls to repel oneanother with a force which exceeds the ambient pressure on the outsideof the container and inflates it.

Preferably, the container is substantially devoid of air so as to form agood heat insulator.

A wall capable of containing a gas in a balloon is formed by joining aplurality of the electrostatically-inflatable containers side-by-side.It is preferred that the polarity of the field in each container isopposite to the polarity of the fields in adjacent containers so thatthe field polarity alternates in successive containers.

One particular such wall preferably is transparent to sunlight andnear-infrared radiation so as to transmit radiant energy to heat a gasin the balloon or other structure and insulate the gas or structure fromheat loss through conduction.

This wall is used to advantage to form at least the upper part of alighter-than-air gas enclosure for a high-altitude balloon, so as tofacilitate a daytime heating of the gas and nighttime insulation againstheat loss.

Preferably, a balloon is provided with a reflective lower surface foruse in a communications system.

Also, it is preferred that the balloon's differential pressure ismaintained at a constant level by pumping in or venting outside air sothat the reflective lower surface is free from distortion which might becaused by expansion or contraction of the gas.

A preferred global communications system is described that is based on aconstellation of high-altitude reflectors, called the earthstratospheric array (ESA). These communications platforms arelighter-than-air craft that have convex-shaped, microwave- and/oroptically-reflective lower surfaces. Ground-to-ground communications ismade possible by reflecting signals off of the High-altitude reflectors.

The reflected signal is dispersed over a wide area of the Earth'ssurface when a nearly collimated beam, originating from the ground, isfocused on the reflector. When the beam reaches the reflector it shouldhave a diameter that is approximately the same diameter as thereflector. Collimated beams are generated by steering, ground-based,high-gain antennas or optical signal sources.

Pointing information for the ground transmitter/receiver is derived fromthe Global Positioning System (GPS). Additionally, microwave antennas oroptical sensors, located on the perimeter of the high-altitudereflector, may be used to measure signal strength and to correct forsteering vector errors due to atmospheric refraction of the microwave oroptical signal.

The global communications system is predominantly a broadcast system;however, bi-directional communications is possible; although, at a muchlower data rate in the outbound direction, from the individual user'sperspective. The content of broadcast information may be controlledlocally. Signals are broadcast during temporal “windows-of-opportunity”when a high-altitude reflector is within range. Coverage becomes morecomplete as more reflectors are added to the ESA.

A high-altitude reflector craft predominantly moves with the wind;however, a limited amount of controlled movement is possible. Alightweight annular truss forms the primary structure of thehigh-altitude reflector. Two propellers, located on opposite sides ofthe annular truss, are used for propulsion. Propulsion may be used tomaintain a fixed position, move in a direction that maximizes theseparation between adjacent high-altitude reflectors, or to travel to adesired landing site.

The balloon is constructed with an “electrostatic balloon skin”consisting of rows of oppositely charged cavities, made with reinforcedpolymeric sheets that have electrically conducting inner surfaces. Whenthe cavity is sufficiently charged, and when the balloon reaches asufficient altitude, the skin is inflated. It has a near vacuum inside,thus forming a thermally insulating layer and also reducing the densityof the skin. The altitude of the balloon is maximized by solar heating.The interior gas is heated during the daytime. The insulating skin helpsto retain the heat during the nighttime.

Preferably, power is transmitted to the balloon by microwave beams fromthe ground. Antennas are provided in the lower portion of the balloon toreceive the power.

A rechargeable battery is used to store a portion of the microwaveenergy that is received from the ground. A hydrogen fuel cell providesan alternative source for charging the battery. Power is required forpropulsion, charging the electrostatic balloon skin, and for operatingother communications and control subsystems.

The high-altitude reflector has two balloon chambers. The upper chambercontains helium gas. The lower chamber is filled with native air.Outside air is pumped into or vented from the lower chamber to maintaina constant pressure, while maintaining a constant overall balloon shape.This minimizes stress in the balloon skin, thereby increasing thelifetime of the craft. By operating at a relatively lower internalpressure, the internal gas density is reduced and the overall balloonweight is reduced. This increases the maximum altitude that can beattained and maximizes the communication coverage area.

Insulated pressure vessels are evenly distributed around the annulartruss. Prior to liftoff, most of the pressure vessels are filled withliquid helium. A few of the pressure vessels are filled with liquidhydrogen. At liftoff, the lower chamber is fully filled with heatednative air and the upper chamber is completely empty. Initially, thecraft is functioning entirely as a hot-air balloon.

The pressure differential (inside-to-outside pressure), altitude, andascent rate are monitored by pressure sensors. As the craft starts toascend, warm helium is released into the upper chamber to maintain lift.The helium is boiled and heated by burning a portion of the hydrogen. Asthe air in the lower chamber expands, a portion of the air is vented tothe outside to maintain a constant differential pressure. All of thehelium has been boiled off and the helium tanks are nearly empty whenthe craft reaches its desired altitude (e.g., 100,000 ft.).

Only one-third of the liquid hydrogen is burned off to heat the heliumgas. When the craft first reaches the desired altitude the remaininghydrogen is still in liquid form. However, the hydrogen will continue toslowly boil off and become gaseous. Valves are closed to prevent anyfurther release of gas into the balloon's upper chamber. Other valvesare opened to allow the hydrogen gas to fill the nearly empty vessels,previously filled with liquid helium. The gas pressure will increase asmore hydrogen is converted to gas. The hydrogen gas pressure is at themaximum rated pressure of the gas storage vessels when all of thehydrogen is converted to a gas.

After the foregoing procedure, the craft has been lofted to the desiredaltitude while maintaining a substantially constant pressuredifferential and balloon shape. The fuel storage tanks are at maximumpressure, full of hydrogen gas. Hydrogen gas is the primary source ofenergy for powering the High-altitude reflector.

The electrostatic balloon skin is charged when the craft reaches a highaltitude (about 70,000 ft.). A relatively low external pressure isrequired in order to inflate the electrostatic balloon skin. At lowaltitudes the pressure is too great to inflate the skin. TheElectrostatic Balloon Skin provides an insulating layer that helps tomaintain a relatively warm internal temperature.

It is believed that the electrostatic balloon of the invention iscapable of reaching and maintaining a significantly higher altitude thanis possible for a conventional balloon, where the internal and externaltemperatures are the same.

Controlled descent can be accomplished by discharging the electrostaticballoon skin and allowing the internal temperature to equalize with theexternal temperature. Cold native air is pumped into the lower chamberto maintain a constant differential pressure. To slow the decent priorto landing, hydrogen is burned to heat the interior air. Once on theground, the helium in the upper chamber is pumped out and recovered forrecycling.

System equipment (i.e., power generation, communications, and guidanceand control) are co-located on a “systems platform.” The systemsplatform is physically located on the centerline and near the bottomwithin the balloon's lower chamber. The systems platform is suspended bysupport rods from the annular truss. This configuration helps to lowerthe overall center-of-gravity of the craft. A low center-of-gravitymakes the craft inherently more stable.

Prior to filling the balloon, the craft can be assembled in a hangerthat has a relatively low ceiling, a significant logistic advantage. Thecraft can be handled by the external annular truss during the launch andrecovery processes, a significant practical advantage.

The foregoing and other objects and advantages of the invention will beset forth in or apparent from the following description and drawings.

IN THE DRAWINGS

FIG. 1 is a schematic diagram of a communications system constructed inaccordance with the present invention;

FIG. 2 is a schematic representation showing the dispersion and locationaround the world of high altitude reflectors used in the system shown inFIG. 1;

FIG. 3 is a partially schematic, partially broken away side elevationview of a high altitude balloon which can be used in the communicationsystem illustrated in FIGS. 1 and 2;

FIG. 4 is a perspective view of a portion of the structure of theballoon shown in FIG. 3;

FIG. 5 is a perspective schematic view of another portion of the balloonstructure of FIG. 3;

FIG. 6 is a perspective view, partially schematic, of electronic controland other equipment used in the balloon of FIG. 3;

FIG. 7 is a schematic block diagram of the mechanical and electricalsystem of the balloon of FIG. 3;

FIG. 8 is a partially schematic top plan view of a segment of the skinof the balloon shown in FIG. 3;

FIG. 9 is a schematic perspective view of the skin structure of theballoon shown in FIG. 3;

FIG. 10 is a schematic view illustrating the electric field lines forthe skin of the balloon shown in FIGS. 3 and 9;

FIG. 11 is a partially schematic exploded perspective view of a portionof the balloon shown in FIG. 3;

FIG. 12 is an elevation view of the structure of FIG. 11;

FIG. 13 is a perspective view, partially schematic, of a component ofthe structure shown in FIGS. 11 and 12;

FIG. 14 is an electrical schematic view of a portion of the powercollection system of the balloon shown in FIG. 3; and

FIG. 15 is a schematic perspective view illustrating the operation ofthe electrostatically inflatable structure of the invention.

COMMUNICATIONS SYSTEM AND METHOD

The major components of the global communications system 20 areillustrated in FIG. 1. The central component is a saucer-shapedhigh-altitude reflector 22. This component is an oblate spheroid-shapedlighter-than-air craft or “balloon” intended to navigate in thestratosphere for relatively long periods of time and to facilitateground-to-ground communications. Its convex lower half 24 serves as adispersive reflector for microwave and/or optical signals. A collimatedmicrowave beam 26 transmitted from a steering high-gain antenna 28reflects off of the lower surface 24 of the high-altitude reflector. Thereflected beam pattern is broad and covers a substantial area on theearth's surface.

A GPS satellite 30 is representative of the existing network of GPSsatellites that transmit position location data. Signals from four ormore GPS satellites provide the necessary information for a GPS receiverto calculate its precise location (i.e., latitude, longitude, andaltitude) of the balloon 22. Similarly, GPS may be used to determine thelocation on the ground of the steering high-gain antenna 28. The GPSlocation of the high-altitude reflector is transmitted to the ground.The two locations are used to calculate the steering vector that focusesthe collimated microwave beam on the reflector 22. As the high-altitudereflector moves in 3-dimensional space, the steering vector iscontinuously recalculated and the antenna is steered to follow itsmovement, or to lock onto another reflector.

Atmospheric conditions can cause refraction (bending) of the microwavebeam. This bending can cause the beam to partially or entirely miss thereflector 22. Refraction is largest when the beam is at low angles overthe horizon. This effect is beneficial for some communications systems.Refraction bends a propagating electromagnetic wave over the horizon andhas the effect of extending the range beyond the expected line-of-sightrange. For the proposed system, refraction is not necessarilyadvantageous. This potential problem can be mitigated by measuring thesignal power on opposite sides of the reflector and adjusting thesteering vector to balance the signal power levels between the twoantennas.

Wideband signals are transmitted from the steering high-gain antenna 28to individual users via the high-altitude reflector 22. Information mayoriginate from a wide variety of institutional sources or from otherindividual users. Types of information include: entertainment,education, news, software, financial data, publications, and businesscommunications. Information from various sources is collected via alocal area network (LAN) 32, electronically combined, and is broadcastto individual users. Individual users are capable of receiving any ofthe broadcast information; however, in practice users usually will onlydecode and store wanted and authorized information.

An individual user receives the microwave signal with anomni-directional antenna 36 attached to a personal electronics device(PED) 34, as an example. The microwave signal transmitted by the antenna28 is received by any user PED that is within the receiving area.Similarly, multiple steering high-gain antennas may use a commonhigh-altitude reflector to broadcast their microwave signals. However,to prevent interference, some form of multiplexing usually is necessary(i.e., time-division, code-division, space-division, or frequencydivision multiplexing).

Individual PEDs may directly transmit back to a steering high-gainantenna operating in the receive mode; however, the system gain is muchlower than with the antenna 28 because the transmit power of the PED ismuch lower and its signal is transmitted in all directions. Thissuggests that the steering high-gain receivers should have either muchhigher gain or be much more sensitive than the broadcasting high-gainantenna 28. One simple way to make a receiver more sensitive is to limitthe bandwidth. Receiver sensitivity is inversely proportional to thereceiver bandwidth.

The same basic communications concept may be employed with an opticalsystem. In an optical system, a moderately powered laser may be used toilluminate the high-altitude reflector with a collimated optical beam. Aphotodiode or avalanche photodiode (APD) is used to receive the opticalsignal. In the reverse direction the individual user may use a low-powerdefocused laser to transmit a signal to a high-gain optical receiver. Amixed mode system, i.e., one using both laser and microwave beams, alsois possible. Microwave and optical systems may be transmittedsimultaneously and without interference via a common high-altitudereflector 22.

If an individual user desires to transmit wideband information, heshould do so by accessing a LAN connected to a local steering high-gainantenna or by transmitting via some other higher bandwidth method suchas satellite, or fiber-optic land lines. This bandwidth limitation inthe outgoing direction usually will not be a serious disadvantage due tothe fact that individuals are usually much bigger “information sinks”than they are “information sources.” TV, movies, newspapers, books,technical reports, and computer software are examples of informationthat might be commonly broadcasted over a wideband channel. These formsof media provide information that is generally useful to a-large numberof individuals. In contrast, electronic mail from individuals typicallycontains much less information and may be transmitted at a much lowerdata rate.

The bandwidth of the broadcasted transmissions may also be limited bythe signal dispersion caused by the texture of the balloon skin andmulti-path effects. Signal drop-outs may also be common occurrences.This limitation may be partially overcome by providing a capabilitywithin a PED to repair media content by direct sharing via an infraredlink (similar to a set-top Remote Control), a short-range wirelesstransceiver, or LAN access. This will require that PED hardware andoperating systems be planned and designed from the start with the“data-repair” feature. For example, if a homework assignment has notbeen fully received, it may be completed by communicating with othernearby PEDs. Alternatively, information may be broadcast multiple timesand the data-repair feature reconstructs the complete file from segmentsof separate transmissions.

For a steering high-gain broadcast antenna to be linked with a user, ahigh-altitude reflector must be in a suitable location in thestratosphere to support the connection. The coverage area is generallyincreased as the altitude of the reflector is increased. Also, the totalnumber of reflectors that are required to cover the entire planet isreduced as the altitude is increased. It is also advantageous to haveseveral high-altitude reflectors within range at the same time so thatcommunications is almost continuous.

However, continuous communications is not essential for the system to beuseful, especially in the initial phase of deployment. Newspapers andmail are typically delivered only once a day. TV, movies, and bookscould be downloaded in response to an order, recorded, and then read ata later time that is convenient for the user.

Alternatively, it is not always necessary to view new material as soonas it is received. With the increased capacity and low cost ofelectronic memory, it is possible to store information for days or weeksbefore it becomes available for use. The item is received and then liesdormant until the predetermined time arrives for its emergence. Examplesof this type of information include: episodes in a series, lessons in acourse, devotionals in a study, and books in a series. Any informationthat is not highly time sensitive could appear to be delivered on aregular interval even though the arrival is spotty and random. The keyis to send it early.

FIG. 2 shows an “earth stratospheric array (ESA)” 40 which is anorganized constellation of high-altitude reflectors 22. It is envisionedthat new reflectors can be deployed at appropriate times and locationsto fill any gaps in the ESA.

High-altitude reflectors in the form of balloons generally follow thehigh-altitude wind patterns; however, they are capable of slowlynavigating according to a centrally-controlled plan. The flight path ofhigh-altitude reflectors is continuously adjusted to provide the mostuniform coverage of the world by the ESA. Maintaining a substantiallyuniform coverage while conserving energy can be enabled with the aid ofa computer simulation (at a central control center on the ground) tooptimize the ESA. Furthermore, the status and condition of eachhigh-altitude reflector is continuously monitored. When a high-altitudereflector is nearing the end of its flight time, it is commanded to landnear a depot facility for maintenance, repair, and redeployment intoservice.

The number of high-altitude reflectors needed to provide 100% coverageof the Earth can be determined as follows: The earth's surface has anarea of 1.71×10⁸ km². At an altitude of 100,000 feet and a maximumcoverage angle on the ground of 15 degrees per reflector, the coverageradius is 114 km or 71 miles. If there is an average of 3 reflectorswithin this area, then the entire planet can be covered withapproximately 12,583 reflectors. If an altitude of 160,000 feet could beachieved, then less than 5,000 reflectors would be needed.

Revenues can be collected by planning from the outset to implement asystem that uses a combination of data encoding, transmission and PEDhardware, and a PED operating system that allows downloaded items to belinked with advertisements for a specified length of time. For example,a product or service provider agrees to pay the owner of the copyrightedmaterial for the global or regional distribution rights. Theadvertisement is linked to the copyrighted material in a way thatprevents the two from being separated for a specified period of time.When the period of time is complete (i.e., the owner of the copyrightedmaterial has been paid in full) then the embedded advertisement(s) willautomatically become inert.

High-Altitude Balloon

The high-altitude reflector balloon 22 shown in FIG. 1 is shown ingreater detail in FIG. 3. The balloon's preferred diameter is around 50meters and its skin is comprised of “electrostatic balloon skin” whichis described in detail below. Its upper hemisphere 41 issemi-transparent to facilitate heating from the sun. Its lowerhemisphere 24 is reflective to both microwave and optical beams.

A stiff annular truss 42 supports the balloon's perimeter. An internalflexible diaphragm 44 separates an upper cavity 46 from a lower cavity48. The upper cavity 46 is filled with helium (He) gas, while the lowerhalf is filled with native gas (air). Alternatively, hydrogen (H₂) gascould be used instead of helium gas; however, it is a far more dangerousgas. The lower cavity 24 is filled with ambient air. Air is vented fromthe lower cavity or pumped into the lower cavity via an air duct 50. Theballoon skin is broken away to show the air duct and nearby structure.

The annular truss serves several purposes. It helps to maintain acircular cross-sectional shape for the balloon, even under moderate windloading conditions. This helps to maintain a symmetrical and sphericallyshaped reflector. It also provides a structure for mounting thrusters,antennas, cabling, sensors, gas and fuel storage, and a docking port. Italso provides an external structure that is very useful during theconstruction phase, deployment phase, docking maneuvers, and therecovery phase (e.g., towing).

The annular truss 42 (details of which are shown in FIGS. 4 and 5) ismade of very thin aluminum tubing or filament wound composite material52 (similar to the material used in fishing rods). The annular truss isextremely lightweight and strong. Distributing the load on the trussevenly is done to prevent flexing the truss beyond its design limits.

Referring to FIG. 4 as well as FIG. 3, thermally insulated pressurevessels 54 are evenly distributed around the annular truss. Prior toliftoff, most of the pressure vessels are filled with liquid helium. Afew are filled with liquid hydrogen, used for fuel.

Referring to FIG. 5, the balloon walls consist of three parts: (1) theskin 56 of the upper hemisphere; (2) diaphragm 44; and (3) skin 48 onthe lower hemisphere. Each one of these walls is bonded together withthe others at the joint 60 to form an air-tight seam. The upper andlower walls are reinforced with strength members consisting of smallbraided ropes made of a high-strength, light-weight synthetic fiber likeVectran™ or Spectra™.

The upper skin 56 is attached to the truss 42 by folding it around theinnermost horizontal truss member 62 and attaching its strength membersto form a loop around the member 62. Conductors within the upper andlower skin layers are terminated with conductive grommets 64. Anelectrical wiring harness 66 is connected to these grommets for chargingthe electrostatic balloon and for power collection.

FIG. 6 shows the electrical power and control system 68 for the balloon22. The components are mounted on a systems platform 70 which issupported on the vertical centerline of the balloon by stiff rods ortubes 72 attached to the truss 42. The rods 72 are evenly distributedaround the perimeter of the annular truss 42 to distribute the load.Preferably, the lower skin 48 is attached to the rods 72 to help holdthe hemispherical shape of the lower hemisphere 48.

The system 68 includes: a system processor 74; a thruster control unit76 for servo drivers 122 (FIG. 7) for the propulsion units; a microwavepower converter 78; a communications interface unit 80; an air pump andgas heater 82; pressure sensors 84; a rechargeable battery 86; ahydrogen fuel cell 88; and a high-voltage charge pump 90.

Method of Manufacture

Assembly of the craft can be done in a large airplane hanger or othersuch building. For example, the Boeing 747 airliner has a wing span of64.4 meters and length of 70.7 meters. Its tail height is 19.4 meters. Ahanger used for servicing a Boeing 747 may be adequate for assembling ofthe high-altitude reflector. Large aircraft hangers are already in placeall over the Globe.

Preferably, in an example of the method of manufacture, the annulartruss 42 is assembled first. It is supported by floor stands evenlydistributed in a circle. The stands raise the truss to eye level. Thepre-assembled balloon is attached to the truss. A long tent-likestructure is used to provide an access path to the center. Thepre-assemble systems platform is installed inside the lower chamberthrough a slit in the center of the reflective (lower) surface of theballoon. The slit is sealed later after the balloon is inflated.

As it was explained above, the systems platform and the annular trussare interconnected by flexible support rods 72. During assembly, thesupport rods lay in a common plane. They are curved in a spiral shape sothat the systems platform is at the same height as the annular truss.When the balloon is inflated the systems platform is allowed to rotate.The rods straighten and the systems platform moves into a suspendedconfiguration, below the annular truss 42. This construction methodallows the high-altitude reflector balloon 22 to be easily assembled andtested in a controlled environment, without the need for specializedequipment or large scaffolding.

Propulsion System

Referring again to FIG. 3, two propulsion units in the form of fans 104and 106 are mounted to the annular truss 42 on opposite sides of theballoon. These fans are used to rotate the balloon to the desiredheading, and also are used to propel it forward in a desired direction.A compass is used to measure the orientation of the High-altitudereflector relative to the Earth's magnetic field. The fans have variablespeed motors and servo drivers 122 (FIG. 7) which are used to controlrotation and forward motion under control of the systems processor 68(FIG. 6).

Preferably, the fans 104 and 106 are oriented to direct their thrustparallel to each other and in the plane of the annular truss 42, andsteering the balloon is achieved by varying the directions and speeds ofthe fans relative to one another. Alternatively, as a backup system,hydrogen-burning jets can be used instead of fans, if needed.

The balloon 22 is made inherently stable by placing the systems platformlow and at the center of the craft. Although wind gusts and use of thethrusters may rock or tilt the craft, because the reflector is sphericalin shape, the affect on communications is believed to be relativelysmall and inconsequential.

The components on the systems platform 70 are partially protected bybeing inside the balloon 20. The systems platform is at least partiallyprotected from sun loading, moisture, atmospheric electrical activity,and atmospheric contaminants.

Electrostatic Balloon Skin

The primary function of the electrostatic balloon skin which forms theoutside wall of the balloon is to thermally insulate the interior gasfrom the ambient atmosphere. The electrostatic balloon skin is made of“ribs” which are good thermal insulators because they are enclosureswhich contain a near vacuum.

When the sun is shining, the interior of the high-altitude reflector 22is heated as if it were a large greenhouse, storing and retainingradiated energy from the sun. The thermally insulating electrostaticskin helps the balloon to retain much of that energy which otherwisewould be lost at night.

The purpose of the interior diaphragm 44 is to conserve the helium orhydrogen gas in the upper cavity 46 while maintaining an overallconstant balloon pressure and shape. Native air is vented as theinterior gas is heated and pressurized during daytime, and is and pumpedin to maintain pressure when the interior gas cools at night.

FIG. 7 is a mechanical and electrical schematic of the high-altitudereflector or balloon 22. There are three major components: (1)structural ring or truss 42; (2) systems platform 20; and (3)electrostatic balloon skin for the upper hemisphere 94 and lowerhemisphere 96. GPS receivers 98 and 100, microwave antennas 102,propulsion units 104 and 106, and pressure vessels 54 (FIG. 4) forhydrogen fuel storage are mounted to the structural ring or truss 42.The GPS receivers 98 and 100 are mounted on opposite sides of the trussfrom each other. The two fans 104 and 106 also are mounted on oppositesides of the truss from each other. They are driven by servo-drivers 122under the control of the systems processor 74. The four microwavereceivers #1 through #4 are mounted to the structural ring, equallyspaced, one in each quadrant of the circle defined by the ring. Thepressure vessels 54 also are uniformly spaced around the structural ringto distribute the load.

As noted above, the electrostatic balloon skin is comprised of twoparts: (1) upper hemisphere skin 94; and (2) lower hemisphere skin 96.Both hemispheres are formed of electrostatic balloon ribs 108 (FIG. 8)that extend from the structural ring toward the poles 110 and 112 of thespherical balloon (FIG. 3).

FIG. 8 is a section of the lower hemisphere skin showing the pole 112 ofthe lower hemisphere and the structural ring (truss) 42.

All electrostatic balloon ribs have a constant width (except at theends). All of the ribs are electrically connected to one of twohigh-voltage buses 142, 126 at the structural ring. One high-voltage bushas a positive charge, while the other has an equal but opposite charge.These charges serve to inflate the hollow ribs, as it will be explainedbelow.

Each rib is a sealed container having opposed conductive surfaces. Thewall structure is made by forming conductive coatings where needed onthin thermo-plastic sheets, laying one of the sheets on the other withthe conductive areas properly oriented, rolling the sheets or otherwiseforcing the air out from between the sheets, and heat-sealing the sheetstogether to form joints between, the ribs and end closures for the ribs.

FIG. 9 shows a section of electrostatic skin with ribs 108 inflated. Theinterior 116 of each is almost a vacuum.

As it is shown in FIG. 10, the polarity of the electrostatic balloonribs alternates between adjacent ribs. A positively charged rib isalways preceded and followed by a negatively charged rib. The polarityof adjacent rows of electrostatic balloon ribs is alternated because ifall of the ribs had the same polarity, then the electric field lines118, 120 would not extend into the interior of the balloon. Coulomb'sLaw dictates that the electric field is zero within a conductive spherethat has a uniform electric charge. This would defeat the purpose ofinflating the balloon skin with electric charge. By alternating thepolarity of adjacent rows, this problem is solved. Electric field linesclose between adjacent rows. The electric field at a distance from thesurface of the balloon is zero (in the “far field”). Also, the netcharge for the high-altitude reflector is near zero. (The balloon'scharge is neutral). Thus, an external current source is not required tocharge the electrostatic balloon.

Making the balloon neutral will reduce the attraction of dust and dirt.If the outer surface of the balloon is contaminated with a sufficientquantity of charged particles the electrostatic balloon will beneutralized. Neutralizing the outside layer of the electrostatic balloonrib may cause it to deflate. It may be advantageous to periodicallychange the polarity of each row to throw off any contaminants that havean electric charge.

It may also be advantageous to periodically totally discharge all of theelectrostatic balloon ribs to purge any gas that may have leaked intothe element via the osmosis process or to detect leaks. This is possibleby using small one-way valves (not-shown) located at the end of eachrib. A flow sensor might also be useful. A valve and flow sensor can beimplemented with micro-electro-mechanical systems (MEMS) technology.Measuring the high gas flow would indicate the presence of leak. If aleak could be detected and isolated to an individual rib then it may bepossible to repair or reduce the leak by simply not inflating (notcharging) the rib.

The electrostatic balloon skin is inflated with an electric charge froma high-voltage source or charge pump 190 (FIGS. 6 and 7) located on thesystems platform 70. The high-voltage lines or buses 124, 126 are routedalong one of the support rods 72 (FIG. 6) and then around the annulartruss 42. Each of the buses is electrically connected to every otherelectrostatic balloon rib. The inner opposed walls of all of theelectrostatic balloon ribs is electrically conductive, but electricallyisolated from the adjacent rib at the seams. The electric charge willdistribute itself over the entire length of a rib due to the repulsiveforce of like charges. Similarly, opposed charges within a rib willforce apart the outer and inner layers of the rib, thus inflating it.

At lower altitudes the charge usually will not be sufficient to overcomethe high atmospheric pressure acting on the outer surface of the rib.However, at high altitudes the atmospheric pressure will be lower andthe force applied by the electric charge will be sufficient to inflatethe rib. If the rib is reasonably air tight, then a near vacuum willexist inside the rib. This makes the rib a good thermal insulator.

The balloon layers from top-to-bottom are illustrated in a schematicperspective view in FIG. 11. The two upper layers 120, 130 form the ribsin the upper hemisphere of the balloon (shown connected by dashedlines). Similarly, the two lower layers 132, 134 form the ribs in thelower hemisphere of the balloon (also shown connected by dashed lines).The thin layer in the middle represents the diaphragm 44 (FIG. 3). thatseparates the upper cavity containing helium from the lower cavity 48containing native air. FIG. 12 is an end elevation view of the structureof FIG. 11.

The outer surfaces of the electrostatic balloon ribs (upper and lower)and the diaphragm layer are made of oriented polyester, or Mylar™. Thismaterial is commonly used in party balloons. It is strong, chemicallystable, lightweight, easily bonded, readily available, and relativelyinexpensive.

The internal surfaces of the walls forming the ribs in the upperhemisphere are coated with thin electrically conductive layers 138 thatare transparent to visible light and energy in the near-infrared portionof the spectrum. Thus, energy from the sun readily heats the interiorthrough the electrostatic balloon skin in the balloon's upperhemisphere. The interior gas retains most of its heat because the heatlost due to radiation is very small, at moderate temperatures (e.g.below 100° C.), and the heat lost due to conduction is small, becausethe charged electrostatic balloon skin is thermally insulating. Thiseffect is called the “greenhouse effect.”

Reflective Balloon skin

The electrostatic balloon ribs in the balloon's lower hemisphere have adifferent construction. The interior side of the lower surface has arelatively thick, reflective layer 140 of copper. Copper is used becauseit is electrically conductive, very ductile, abundant, and relativelyinexpensive. The thickness of this layer is slightly less than thetheoretical skin depth of the electrical current at the microwavefrequency that is intended to be reflected by the high-altitudereflector. Most of the microwave energy is reflected off of thehigh-altitude reflector. However, a portion of the energy is allowed tobe transmitted through this layer 140. The ratio of reflected andtransmitted energy can be controlled by adjusting the thickness of thecopper layer. The copper at the edges 139 does not extend into the seamregion between adjacent ribs. Otherwise, an electrical “short” wouldoccur.

The frequency of interest is 3 Gigahertz (GHz) to 10 GHz in themicrowave band. This is described as the SHF band. It is also known asthe X, C, and S bands, as defined by the Institute of ElectricalEngineers (IEEE). This range of frequencies is desirable because it isnot significantly affected by the weather. Attenuation due to fog andclouds becomes significant only above 30 GHz. Attenuation due to rainbecomes significant above 10 GHz. The reflective copper layer should be0.003 to 0.005 inches thick, to reflect most of the microwave energy butto allow some of the energy to pass through to the inner powercollection layer. The width of the rib should be at least one wavelengthto serve as an efficient reflector. The wavelength at 3 GHz is 10centimeters (cm). The wavelength at. 10 GHz is 3 cm. Therefore, for thewavelength range of greatest interest the electrostatic rib is at least3 cm wide.

Power Collection

A power collection structure 142 is shown schematically in FIG. 13, aswell as FIGS. 11 AND 12. The structure 142 consists of a series ofdipole antennas 144 and a transmission line 146 formed of very thinlayers of copper. This configuration is known as a “curtain antenna.”The insulating layer 132 (FIG. 12) between the antenna elements isconductive but it has a relatively high resistance sufficient to allowthe static electric charge to distribute and collect on the inner layerof the electrostatic balloon rib without shorting out the microwavepower collection circuit.

FIG. 14 is a schematic diagram of a power collection circuit 150. Powercollected by each of the individual electrostatic balloon ribs isrectified by a rectifier circuit 152, summed, and distributed along apower collection transmission line 154 that runs along the perimeter ofthe annular truss. This power is filtered and converted by converters156 to a DC voltage that is suitable for charging the battery and use bythe various subsystems.

The efficiency of this power collection method is diminished by a numberof factors. These include: orientation of the dipole antenna elementswith respect to the wave front; wavelength mismatch; destructiveinterference between dipole antenna elements; and loss in the partiallyinsulating layer. Assume that the power collection has an efficiency of40 percent. Assume that the reflective layer reflects 80% of themicrowave power and transmits 20% of the power to the inner surface ofthe lower layer. Then 8% of the total power is collected. If fifty localtransmitters are focused on a High-altitude reflector and eachtransmitter has a total power of 200 watts then the total powerimpinging on the reflector surface is 10 kilowatts. Eight percent of 10kilowatts is 800 watts of collected power. This should be more thanenough to maintain the electric charge in the electrostatic balloon skinand to operate all of the craft's subsystems, under normal conditions.

While the power collection efficiency is only 40 percent, the energy isnot lost. The 60 percent portion of the power that is not collected ismostly lost as heat. This represents a 1-kilowatt heat source within theballoon that has no weight penalty. This heat source is not verysignificant when compared to the solar heating effect during the day.However, it is present during the nighttime, as long as the craft isover a populated area. This external heat source will help to offsetheat loss during the nighttime and also help to conserve the hydrogenfuel and extend the time that the craft can stay aloft.

Energy may also be collected from the sun during the day by usingconventional arrays of solar cells mounted on the structural ring 42 orby using photovoltaic devices embedded in the balloon skin. It is alsopossible to recover and reuse the energy that is stored in theelectrostatically charged skin.

Mathematical Model of Balloon Flight

A mathematical model and computer simulation was constructed for ahypothetical high-altitude reflector to show that a practical systemcould be constructed and operated for an extended duration at analtitude of 100,000 feet. The model includes dimensional and weightestimates for every component. Some of the model parameters are:Diameter: 50 m Total Height: 126 ft. Total Volume: 2,600,000 ft³ TotalSurface Area: 65,000 ft² No. Truss Segments 172 No. of Aluminum Tubes inTruss: 1,548 Total Weight of Truss: 200 lbs. Total Weight of BalloonMaterial: 3,270 lbs. Combined Weight of Other Items: 1,014 lbs. No. ofHelium Vessels: 32 No. of Hydrogen Vessels: 11 Weight of Helium: 636lbs. Initial Weight of Hydrogen: 124 lbs. Total Initial Weight: 5,244lbs.

The craft starts out on the ground. The ambient temperature is assumedto be 20° C. and the ambient pressure is 760 torr. Initially, there isno helium gas inside the balloon's upper chamber 46 (FIG. 3) and thelower chamber 48 is filled with native air, at a temperature of 29.5° C.

The air is heated and pumped in from an external source (not shown).Thirty-two pressure vessels are filled with liquid helium. Elevenpressure vessels are filled with liquid hydrogen. The total weight ofthe craft, including the heated native air, is 192,000 pounds; however,the displaced air weights 192,567 pounds. This gives the craft apositive buoyancy (or lift) of 567 pounds. The internal pressure is only0.1 percent higher than the external pressure. This difference may notseem very significant; however, applied over the entire surface of theballoon this pressure results in a significant tension in the relativelysmall strength members that are imbedded in the balloon skin. Thedifferential pressure is held constant over the entire flight time ofthe craft.

By starting with most or all of the gases in liquid form, better controlof the ascent of the craft is maintained, but with a minimum of weightand space occupied, as compared with other gas-handling methods forhigh-altitude balloons.

The craft quickly rises as soon as it is released. As the craft ascends,helium gas is released into the upper chamber. The fill rate iscontrolled by boiling off the liquid helium at a rate that maintains asteady lift of approximately 500 pounds for the first 10,000 feet.Native air is allowed to be expelled from the lower chamber as the upperchamber expands. Hydrogen gas is burned to boil off the helium and toheat it to the desired temperature.

At 10,000 feet, the ambient temperature has fallen to 1.2° C. Theambient pressure is 552 torr. 13,274 cubic feet of helium gas, at atemperature of 10.7° C., has been vented into the upper chamber. Anequivalent volume of air has been vented from the lower chamber to theoutside. The craft continues to rapidly ascend with a lift force of 300pounds. The two fans 104 and 106 maintain the craft's direction andprovide the necessary thrust to keep the craft on its predeterminedcourse.

At 20,000 feet, the ambient temperature is −18.2° C. and the ambientpressure is 372 torr. 42,857 cubic feet of helium gas, at a temperatureof −8.7° C., has been vented into the upper chamber. The craft continuesto ascend with a lift force of 200 pounds.

At 30,000 feet, the ambient temperature is −38.8° C. and the ambientpressure is 253 torr. 82,348 cubic feet of helium gas, at a temperatureof −29.3° C., has been vented into the upper chamber. A 200 pound liftforce is maintained. The craft ascends at a faster rate because theaerodynamic drag diminishes as the atmosphere thins.

At 40,000 feet, the ambient temperature is −60° C. and the ambientpressure is 170 torr. 138,842 cubic feet of helium gas, at a temperatureof −50.5° C., has been vented into the upper chamber. Less hydrogen gasis needed to heat the helium as the craft ascends into the extremelycold atmosphere.

At 50,000 feet, the ambient temperature is slightly warmer at −57.3° C.,but the ambient pressure continues to decline. The ambient pressure is128 torr. 225,093 cubic feet of helium gas, at a temperature of −47.8°C., has been vented into the upper chamber.

At 60,000 feet, the ambient temperature is −54.6° C. and the ambientpressure is 87 torr. 392,978 cubic feet of helium gas, at a temperatureof −45.1° C., has been vented into the upper chamber. The lift force isstill 200 pounds.

At 70,000 feet, the ambient temperature is −51.2° C. and the ambientpressure is 57 torr. 648,250 cubic feet of helium gas, at a temperatureof −45.1° C., has been vented into the upper chamber. The lift isreduced to 50 pounds. However, the craft continues to ascend at a fastrate due to the thinning atmosphere. At approximately 50 torr theelectrostatic charge generator is activated to inflate the electrostaticballoon ribs.

At 80,000 feet, the ambient temperature is −46.6° C. and the ambientpressure is 43 torr. 879,259 cubic feet of helium gas, at a temperatureof −32.9° C., has been vented into the upper chamber. A lift of 50pounds is maintained.

At 90,000 feet, the ambient temperature is −42.1° C. and the ambientpressure is 30 torr. 1,326,147 cubic feet of helium gas, at atemperature of −22.1° C., has been vented into the upper chamber. A liftforce of 50 pounds is maintained.

At 100,000 feet, the ambient temperature is −37.4° C. and the ambientpressure is 18 torr. 2,455,984 cubic feet of helium gas, at atemperature of −0.4° C., has been vented into the upper chamber. A liftforce is reduced to 20 pounds. The craft will become neutrally buoyantat slightly above 100,000 ft. There is no remaining helium in the 32helium tanks. However, only 25 percent of the liquid hydrogen has beenconsumed. Valves are closed to the upper chamber and valves are openedbetween the helium and hydrogen tanks. After several days, all of theliquid hydrogen will boil off due to solar heating and pressurize the 43fuel vessels with hydrogen gas. The total volume of hydrogen is 110cubic feet and the resulting pressure is 2,150 psi.

Thus, the empty helium tanks have been used for the storage ofpressurized hydrogen, and the problem of storage of the gas afterchanging from liquid to gaseous form is solved neatly with a minimum ofadded weight and space.

The craft is believed to be capable of operating at approximately100,000 feet for an extended duration. The internal gas is heated bysolar heating during the daytime and the heat is conserved by thethermally insulating electrostatic balloon skin during the nighttime.Microwave power from the ground provides a portion of the electricalpower that is needed to operate the craft. Additional electrical poweris generated by the hydrogen fuel cell.

The craft lands before all of the hydrogen is totally consumed. To beginthe descent, the charge is removed from the electrostatic balloon skinand the internal gas is allowed to cool to the ambient temperature. Asthe craft descends, the pressure will increase. To maintain the constantdifferential pressure, gas is pumped into the balloon. It may benecessary to burn some of the hydrogen to heat the air to slow thedescent. When the craft approaches the ground the last remaininghydrogen is burned to stop the descent for landing.

Mathematical Model of Balloon Structure

A mathematical model for electrostatic balloon elements is set forthbelow. The high-altitude reflector 22 uses elongated electrostaticballoon ribs 108 in the electrostatic balloon skin. For simplicity, thefollowing mathematical analysis is for a simple square-shapedelectrostatic balloon rib. A very thin layer of material is assumed forthis analysis to demonstrate the very unique buoyancy properties ofelectrostatic balloons.

As is shown in FIG. 15, an electrostatic balloon rib 108 is a thinclosed shell of electrically insulating material with an electric chargeinside. The electric charge will evenly distribute over the interiorwall and inflate the balloon. Like charges repel. The resultingelectrostatic force inflates the balloon rib without the use of aninterior gas.

The mass of the stored charge is negligible. The total mass of theballoon rib is the mass of the material use in the balloon skin. Thedensity of the balloon is the total mass divided by the volume. If thestored charge is sufficient to keep the balloon inflated at a givenatmospheric pressure and the balloon density is less than the density ofthe displaced gas, the balloon will rise. If either of these conditionsis not satisfied, the balloon will deflate and fall.

An individual balloon of this type should be inflated at an altitudeabove its critical altitude, rather than being inflated on the ground,where the atmospheric pressure is highest. The balloon will maintain itsshape as long as the charge is present. The balloon will stay afloat aslong as gas does not leak into the balloon. When the balloon drops belowthe critical altitude it will collapse and rapidly fall to the ground.

First, consider LaPlace's Law (for conventional spherical gas-filledballoons):(P _(i) −P _(o))=4T/r.  (1)

Where, P_(i) is the in inside pressure, P_(o) is the outside pressure, Tis the surface tension, and r is the balloon radius. In the case of agasless electrostatic balloon the inside gas pressure is replace by anequivalent electrostatic pressure.

Columb's Law defines the opposing force between two equal electroniccharges:F=q ²/(4πε_(o) r ²).  (2)

Where, F is force, q is the electric charge, r is the distance betweenthe two charges, and ε_(o)=8.85418×10⁻¹² (called the permittivityconstant, with units of coulomb ²/nt·m²)

Atmospheric pressure is the force-per-unit-area exerted by a column ofgas above an area on the Earth's surface. Units of atmospheric pressureinclude inches-of-mercury (″Hg), millimeters-of-mercury (torr),Atmospheres (atm), and pounds-per-square inch (psi). Useful conversionfactors are: 29.92 ″Hg=760 torr=1.0 atm=14.7 psi (average pressure atsea-level).

The density (d) of a gas is given by the expression:d=PM/RT.  (3)

Where P is the pressure in torr, M is the molar mass (dimensionless), Ris the gas constant=62.36 liter-torr/mol-° K, and T is the temperaturein degrees-Kelvin. Add 273 to convert from degrees-Centigrade todegrees-Kelvin. Molar mass is calculated by summing the atomic weights.

The earth's atmosphere is made up of 78% nitrogen (N₂) and 21% oxygen(O₂). The remaining 1% contains inert trace gasses (argon, neon, helium,krypton, and xenon). The molar mass of nitrogen (atomic weight of 14.0)is 2*14=28. The molar mass of oxygen (atomic weight of 16.0). is2*16=32. Earth's atmosphere is not a uniform mix of gasses fromtop-to-bottom; however, since nitrogen and oxygen are close on thePeriodic Chart and the other trace gases are only 1%, the equivalentmolar mass for Earth's atmosphere is approximately 0.78*28 +0.21*32=28.6 grams/mole.

A useful formula for calculating the approximate atmospheric pressure atany altitude is:P=P _(surface) e ^(-h/H).  (4)

Where H is the Scale Height. The Scale Height of Earth's atmosphere isapproximately 7 km or 22,966 ft.

To proceed with the analysis, some arbitrary assumptions are made on thesize, shape, and material of the balloon. Several parameters must becalculated to show the feasibility of an electrostatic balloon concept.These include: the maximum altitude at which the balloon will float, thecharge required to inflate the balloon, the critical altitude at whichthe balloon will collapse and fall, the lift-to-weight ratio at thecritical altitude (i.e., tendency of the balloon to recover to a safealtitude), and the surface tension of the balloon skin relative to thestrength of the material (i.e., the structural integrity of theballoon).

Assume a pillow-shaped balloon with a very thin skin. Assume that theballoon has an average thickness of 1 cm (h) and an equivalent size onedge of 5 cm (both x and y). Assume that the balloon skin material isapproximately 10 nm thick (approximately 10 atoms thick). Assume thatthe skin material is plastic with a specific gravity or 1.4; i.e.,density of 1.4 kg/liter.

For this example, the volume of the balloon is 2.50×10⁻² liter. The massof the balloon is 7.0×10⁻⁵ grams. The density of the balloon is2.80×10⁻³ grams/liter. The maximum altitude of the balloon is determinedby solving for the atmospheric pressure that gives the same density asthe balloon (neutral buoyancy) in equation (3) and substituting thisresult into equation (4), then solving for the altitude; i.e.:h=−log_(e) (dRT/760M)·H=139,402 ft.  (5)

Assume a minimum altitude of 100,000 feet (approximately 19 miles). Thisminimum altitude is still well above the capability of known aircraftand most balloons. What electric charge is required to inflate anelectrostatic balloon at this altitude? The atmospheric pressure at thisaltitude is:P _(max)=14.7 e ^(−(100,000/22,966))=0.19 psi  (6)

Combining equations (2) and (6) yields the expression:P _(max) =F/A=q ²/(4πε₀ r ² A)=0.19 psi.  (7)

The total electric charge is 2q because the charge is divided equallybetween the top and bottom of the pillow-shaped balloon: $\begin{matrix}\begin{matrix}{{2q} = {2 \cdot \lbrack {4{\pi ɛ}_{o}r^{2}{A \cdot 0.19}} \rbrack^{{- 1}/2}}} \\{= {3.82 \times 10^{{- 7}\quad}{couloumb}}}\end{matrix} & (8)\end{matrix}$

A single electron has a 1.60×10⁻¹⁹ coulomb charge. Therefore, theballoon must be charged with 2.39×10¹² electrons to remain inflated at100,000 ft. This may seem like a large number; however, it is not anunreasonably large number of electrons. One ampere (amp) is one coulombper second. The charge required to inflate the balloon is the same asthe charge that flows through a 40-watt light bulb in 1 millionth of asecond (one microsecond).

It is useful to be able to relate mass of an object to its gravitationalpull or weight on Earth. Newton's Law of Gravitation gives the force ofgravity (F_(g)) on an object with mass (m) that is located on or abovethe surface of the Earth:F _(g) =GM _(E) m/r ².  (9)

Where G=6.673×10⁻¹¹ N·m²/kg² (called the Universal GravitationalConstant), M_(E) is the mass of the Earth, and distance of the objectfrom the center of the earth. M_(E)=5.972×10²⁴ kg. If the object is nearthe surface of the earth, r =R_(E)=6.378×10⁶ meters. The acceleration ofgravity on the surface of the Earth (and in the stratosphere) is:g=GM _(E) /R _(E) ²=9.80 m/s ².  (10)

The weight of the balloon is given by the expression: $\begin{matrix}\begin{matrix}{W = {{mg} = {( {7.0 \times 10^{- 8}\quad{kg}} ) \cdot ( {9.8\quad m\text{/}s^{2}} )}}} \\{= {6.86 \times 10^{- 7}{{Nt}.}}}\end{matrix} & (11)\end{matrix}$

One kg·m/s² is equivalent to one newton (Nt), a unit of force. Thisballoon weight corresponds to 1.54×10⁻⁷ pounds or 9.62×10⁻⁹ ounces.

Using equation (5) to calculate the density of the displaced gas at100,000 ft. and multiplying by the volume of the balloon predicts anupward force on the balloon of 5.35×10⁻⁸ ounces. Thus, thelift-to-weight ratio at 100,000 ft. is 5.6. This is a significantlift-to-weight ratio when compared to an aircraft; however, the opposingforces on the electrostatic balloon are very small.

A rough calculation of the maximum surface tension can be made byassuming that the balloon is approximately spherical in shape in thevacuum of space. A circumference of 12 cm corresponds to a diameter ofapproximately 3.8 cm. The charge calculations were based on apillow-shaped balloon that is 1 cm thick. Since the electrostatic forcediminishes with the square of the distance the same charge in a vacuumwill result in a surface tension of 32.7 kpsi (472 kpsi×(1/3.8)²). Thisvalue is within reason for high strength plastics. Furthermore, if itbecomes necessary, increasing the surface area of the balloon canfurther reduce this surface tension.

Foremost, it is important to consider the electrostatic balloon as abuilding block for a larger structure. Just like conventional floatingballoons, an electrostatic balloon will maintain its shape when its skinin under tension; i.e., slightly above its equilibrium altitude.

The above mathematical analysis examined a solitary electrostaticballoon element or rib. The Electrostatic Balloon Element has a verythin skin. It is capable of inflating above a critical altitude. It ispositively buoyant above its critical altitude.

The high-altitude reflector is positively buoyant on its own merits. Itis not necessary for the material that is used in the skin to beextremely thin (as assumed in the math model). The high-altitudereflector will benefit from the slightly increased buoyancy when theElectrostatic Balloon Ribs are inflated; however, it does not depend onthis slight boost for maintaining its altitude.

A self-contained system comprising a single solitary electrostaticballoon element has other possible applications. For example,electrostatically inflated structures can be used in outer space to formlight-weight antenna or other structures for satellites or space craft.However, the high-altitude reflector represents a practical near-termapplication that uses a large number of electrostatic balloon elements.The high-altitude reflector takes advantage of the fact that theelectrostatic balloon elements have a near-vacuum inside. When theelements are inflated above the critical altitude, the skin becomesthermally insulating. This is a substantial advantage of usingelectrostatic balloons in the global communications system of theinvention.

The above description of the invention is intended to be illustrativeand not limiting. Various changes or modifications in the embodimentsdescribed may occur to those skilled in the art. These can be madewithout departing from the spirit or scope of the invention.

1. An electrostatically inflatable structure comprising (a) a sealedcontainer with flexible opposed walls having opposed conductivesurfaces, and (b) a voltage source for applying electrical voltages tosaid surfaces to cause them to electrostatically repel one another whensaid container is in a low ambient pressure environment.
 2. A structureas in claim 1 in which the space between said walls is substantiallydevoid of air.
 3. A structure as in claim 1 joined with at least oneother like structure to form a wall made of such structures.
 4. Astructure as in claim 1 said conductive surfaces being electricallyisolated from one another.
 5. A structure as in claim 1 in which each ofsaid walls is a thin plastic sheet with said sheets sealed together attheir edges.
 6. A structure as in claim 3 forming a skin for ahigh-altitude balloon.
 7. A structure as in claim 1 in which said wallsare substantially transparent to sunlight and/or near-infraredradiation.
 8. A high-altitude balloon having (a) a lighter-than-air gascompartment formed by at least one wall, and (b) said wall having atleast an upper portion including a plurality of compartments joined withone another side-by-side, each having opposed conductive inner wallsurfaces capable of being charged with a voltage to create anelectrostatic field between said wall surfaces.
 9. A balloon as in claim8 in which said upper portion is substantially transparent to sunlightand/or near-infrared radiation.
 10. A balloon as in claim 8 in whichsaid wall has a lower portion comprising a flexible diaphragm to allowthe volume of said gas to expand when heated and contract when cooledand a cover over said diaphragm, said cover having a plurality of saidcompartments.
 11. A balloon as in claim 8, in which said wall has alower portion comprising a flexible diaphragm to allow the volume ofsaid gas to expand when heated and contract when cooled, and anelectromagnetic wave-reflecting cover over said membrane, an annularsupport structure, said wall and said cover being secured thereto, and aplurality of struts secured between said annular support structure andsaid cover to stabilize said cover, said cover being vented toatmosphere to accommodate the gas flows due to flexing of saiddiaphragm.
 12. A balloon as in claim 11 including a heater to heat saidgas, a voltage supply, a propulsion system, a fuel supply for saidheater, a gas supply, and a processor for controlling the operation ofsaid heater, said voltage supply, said gas supply and said propulsionsystem pursuant to pre-programmed information and/or wireless signals.13. A balloon as in claim 10 in which said lower portion of said wallincludes an outermost cover which encloses said flexible diaphragm, saidcover having a surface reflective to electromagnetic radiation, and anannular support member to which said wall and said cover are attached.14. A balloon as in claim 8 in which the polarity of the fields insuccessive areas of said compartments alternates.
 15. A balloon as inclaim 8 in which 'said balloon has a lower wall with an antenna arrayfor receiving electrical power beamed towards said balloon from afar,and a propulsion system using said power to maneuver said balloon.
 16. Acommunications system comprising (a) at least one airborne high-altitudeballoon with a surface reflective of electromagnetic waves beamed upfrom the earth's surface, (b) at least one ground-based transmitter forbeaming electromagnetic communications information towards saidreflector; and (c) at least one ground-based receiver for receivinginformation reflected from said reflector.
 17. A system as in claim 16including a plurality of said balloons deployed at spaced intervals overat least a substantial portion of the earth's surface, each of saidballoons having a wall with at least an upper portion made ofside-by-side electrostatically inflatable containers, each of saidcontainers having opposed conductive internal walls, and a voltagesource for supplying an electrical voltage to create an electrostaticfield between said walls of each of said containers, the polarity ofsaid field alternating from one of said containers to the next.
 18. Asystem as in claim 17 including a GPS for locating each of said balloonsand aiming said transmitter at a selected one of said balloons.
 19. Amethod of electrostatically inflating an object, said object being acontainer with flexible opposed walls with conductive opposed surfacesapplying an electrical voltage to said conductive surfaces to develop anelectrostatic force of repulsion between said surfaces, and locatingsaid container in an environment with very low ambient pressure, saidforce of repulsion creating an internal electrostatic pressure exceedingsaid ambient pressure.
 20. A method as in claim 19 in which there is aplurality of said containers joined side-by-side to form one wall of aballoon, and said method includes the step of using lighter-than-air gascontainer, at least in part, by said wall, to lift said balloon to anelevation above the earth at which said internal electrostatic pressureexceeds said ambient pressure, each of said containers beingsubstantially devoid of air.
 21. A method for launching a high-altitudeballoon craft utilizing a lighter-than-air lifting gas, said methodcomprising (a) storing at least a major portion of said lifting gas inliquid form in liquid containers on board said craft, (b) convertingsaid liquid into gaseous form and releasing the gas into said balloon toprovide lift, and (c) controlling the rate of said release to regulatethe rate of rise of said balloon craft.
 22. A method as in claim 21 inwhich substantially all of said lifting gas is in liquid form atlift-off of said balloon, and including the step of supplying heated airto said balloon to start it on its ascent.
 23. A method as in claim 21in which said craft also carries a fuel gas in liquid form, andincluding the step of transferring said fuel gas when it changes togaseous form into containers emptied of lifting gas.
 24. A method as inclaim 23 in which said lifting gas is helium and said fuel gas ishydrogen.
 25. A method as in claim 21 in which said balloon has anelectrostatically inflatable skin, and electrically charging said skinto inflate it when said balloon reaches a pre-determined height.